Abstract
Although the nature of the stimulus which causes a spore forming organism to enter the spore state is not known, a number of theories have been advanced, two of which are probably the most widely cited and most readily investigated experimentally. The first of these, advanced by Buchner, 1 holds that the inciting stimulus is to be found in a “local” exhaustion of nutrient material in the presence of an abundance of previously well nourished cell protoplasm. Turro 2 ascribed the cause of spore formation to the accumulation of metabolic by-products.
Some evidence on this subject is afforded by observations made on B. subtilis grown in peptone water of 0.5, 1, 2, 3, 4, and 5% peptone content. Inoculations were made in duplicate from an invigorated broth culture to 50 ml. flasks containing between 10 and 15 ml. of medium at a reaction of approximately pH 6.8. A count of 1000 cells of the inoculum gave 314 spores to 686 vegetative cells. Adequate exposure to oxygen was insured by the shallow layers of the medium. Incubation was at 37°C., the optimum for the strain of B. subtilis used. Smears were made from each flask at daily intervals for 7 days and again at 10 days, after which the observation was discontinued. From each smear, after staining, a total of 500 cells, including both spore and vegetative forms, was counted. There was no appreciable difference between duplicate flasks in either daily counts or total counts. In only 5 instances did the daily counts fail to agree within 15% of the average, and with the total counts the agreement in half the cases was within 2% or less and in no case exceeded 7%. As a matter of convenience the values obtained have been added together for plotting.
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